Comparison of shearbond strength between metal and indirect resin according to the different conditionings / 대한치과보철학회지

PURPOSE: The purpose of this study is to investigate the differences in bond strength of four different indirect composites to the gold alloy and Ni-Cr alloy according to type of metal surface treatment after water storage. MATERIALS AND METHODS: Type IV gold alloy and Ni-Cr alloy were used for casting alloy while four types of indirect composite resins (Gradia, Tescera Sinfony and in;joy) were used in this study. Metal specimens were produced by casting and total of 240 specimens (60 specimens per one indirect composite group) were prepared. After bonding indirect composite resin and undergoing 24 hours of polymerization, customized jig was attached to the metal specimen and shear bond strength were measured using universal testing machine. Also, differences in shear bond strength before and after water storage for 240 hours were also measured. RESULTS: In the measurement of shear bond strength according to the metal surface treatments, bead group showed high strength followed by loop and flatting group (P<.05). After being stored in water bath for 240 hours, Gradia showed statistically significant high bond strength compared to other indirect composite resins in all groups (P<.05). CONCLUSION: Shearbond strength was found to be different according to type of metal surface treatment and type of metal used after storage in water. Further studies need to be developed for clinical practices as three are still problems of microleakage, stain or wear.

Effect of soldering techniques and gap distance on tensile strength of soldered Ni-Cr alloy joint

PURPOSE: The present study was intended to evaluate the effect of soldering techniques with infrared ray and gas torch under different gap distances (0.3 mm and 0.5 mm) on the tensile strength and surface porosity formation in Ni-Cr base metal alloy. MATERIALS AND METHODS: Thirty five dumbbell shaped Ni-Cr alloy specimens were prepared and assigned to 5 groups according to the soldering method and the gap distance. For the soldering methods, gas torch (G group) and infrared ray (IR group) were compared and each group was subdivided by corresponding gap distance (0.3 mm: G3 and IR3, 0.5 mm: G5, IR5). Specimens of the experimental groups were sectioned in the middle with a diamond disk and embedded in solder blocks according to the predetermined distance. As a control group, 7 specimens were prepared without sectioning or soldering. After the soldering procedure, a tensile strength test was performed using universal testing machine at a crosshead speed 1 mm/min. The proportions of porosity on the fractured surface were calculated on the images acquired through the scanning electronic microscope. RESULTS: Every specimen of G3, G5, IR3 and IR5 was fractured on the solder joint area. However, there was no significant difference between the test groups (P > .05). There was a negative correlation between porosity formation and tensile strength in all the specimens in the test groups (P < .05). CONCLUSION: There was no significant difference in ultimate tensile strength of joints and porosity formations between the gas-oxygen torch soldering and infrared ray soldering technique or between the gap distance of 0.3 mm and 0.5 mm.

Correlation between metal-ceramic bond strength and coefficient of linear thermal expansion difference

The purpose of this study was to evaluate the metal-ceramic bond strength (MCBS) of 6 metal-ceramic pairs (2 Ni-Cr alloys and 1 Pd-Ag alloy with 2 dental ceramics) and correlate the MCBS values with the differences between the coefficients of linear thermal expansion (CTEs) of the metals and ceramics. Verabond (VB) Ni-Cr-Be alloy, Verabond II (VB2), Ni-Cr alloy, Pors-on 4 (P), Pd-Ag alloy, and IPS (I) and Duceram (D) ceramics were used for the MCBS test and dilatometric test. Forty-eight ceramic rings were built around metallic rods (3.0 mm in diameter and 70.0 mm in length) made from the evaluated alloys. The rods were subsequently embedded in gypsum cast in order to perform a tensile load test, which enabled calculating the CMBS. Five specimens (2.0 mm in diameter and 12.0 mm in length) of each material were made for the dilatometric test. The chromel-alumel thermocouple required for the test was welded into the metal test specimens and inserted into the ceramics. ANOVA and Tukey's test revealed significant differences (p=0.01) for the MCBS test results (MPa), with PI showing higher MCBS (67.72) than the other pairs, which did not present any significant differences. The CTE (10-6 oC-1) differences were: VBI (0.54), VBD (1.33), VB2I (-0.14), VB2D (0.63), PI (1.84) and PD (2.62). Pearson's correlation test (r=0.17) was performed to evaluate of correlation between MCBS and CTE differences. Within the limitations of this study and based on the obtained results, there was no correlation between MCBS and CTE differences for the evaluated metal-ceramic pairs.

A research on the corrosion resistance of Ni-Cr alloy with different coatings / 实用口腔医学杂志

Objective: To evaluate the corrosion resistance of Ni-Cr alloy with different coatings in neutral and acid saliva by electrochemistry method. Methods: Measured the self-corrosion potential (Ecorr) and polarization resistance(Rp) curves of Ni-Cr alloy models with different coatings in neutral and acid artificial salivas. Results: The Ecorr of the Ni-Cr alloys all showed positive values, the electrochemistry corrosion and galvanic corrosion were not detected. Conclusion: Ni-Cr alloy with titanium nitride coating, gold electroplating coating, gold-paste layer and gold-porcelain blended layer have both anti-corrosion and esthetical function without changing its own property.

Comparison of MRI artifacts caused by Ni-Cr alloy fixed prostheses on different field-strength magnets / 上海第二医科大学学报

Objective To evaluate the influence of different field-strength magnets(1.5 T and 3.0 T)on MRI artifacts caused by Ni-Cr alloy fixed prostheses.Methods The crown,bridge and upper denture fixed prostheses with different thickness were produced by Ni-Cr alloy as test samples,and were one by one put on the centre of water phantom for MR scanning with different field-strength magnets(1.5 T and 3.0 T).The artifact areas on these two field-strength magnets were measured and statistically compared.The plastic prostheses with the same shape and thickness as the test samples were served as controls.Results Ni-Cr alloy fixed prostheses could cause MRI artifacts,and the artifact areas increased with the mass of prostheses.However,no artifact area was found in controls.Compared with those on 1.5 T magnet,the MRI artifact areas significantly increased on 3.0 T magnet(P

Effect of Mutans Streptococcus on Corrosion Resistance of Ni-Cr Alloy / 上海第二医科大学学报

Objective To study the effect of Mutans Streptococcus(S.Mutans) on the corrosion resistance of Ni-Cr alloy. Methods S.Mutans were isolated in TSB,and then 10~(5)10~6 CFU/mL of bacterial population was reached.The self-corrosion electrical current density and the corrosion electrical current potential of Ni-Cr alloy were found from polarization curves under the condition with or without media plus S.Mutans.The surface of Ni-Cr alloy after bacterial corrosion was examined with X-ray photoelectron spectroscopy(XPS) to find out different element contents.(Results)From polarization curves,it could be found that the self-corrosion electrical current density and the corrosion electrical current potential of Ni-Cr alloy without S.Mutans were 53.5 ?A/cm~(2)and-62 mV,and those with S.Mutans were 75.7 ?A/cm~(2)and-220 mV.Examination of XPS showed that besides Ni and Cr,the element of chlorine(Cl),sulphur(S),calcium(Ca) could be found on the surface of Ni-Cr alloy after bacterial corrosion.(Conclusion Because of) the metabolism of S.Mutans,an oxide film could be destroyed and a biofilm be formed on the surface of Ni-Cr alloy.Bacterial corrosion could lower the corrosion resistance performance of Ni-Cr alloy.

Effect of Heat Treatment with Sol-gel Method on Surface of Ni-Cr Alloy after Coating Ti / 上海第二医科大学学报

Objective To study the effect of heat treatment with sol-gel method on the surface of Ni-Cr alloy for PFM after Ti coating. Methods To establish the sol-gel method of Ti coating on the surface of Ni-Cr dental casting alloy for PFM(pre-treatment for the surface of Ni-Cr alloy,preparation of sol,coating,heat treatment) and to evaluate the color and fragmentation of 10 materials after heat treatment by ISO 10289. Results When kept at a higher condensation temperature and held for a longer time,the materials had less fragmentation.A higher agglutination temperature and a longer time made the materials look deep.When the condensation process was heat treated at(200 ℃) for 2 h and the agglutination process at 450 ℃ for 2 h,the thin film of Ti combined firmly with the surface of Ni-Cr alloy. Conclusion The procedure for heat treatment of Ti coating will affect the level of oxidation reaction on the surface of Ni-Cr alloy,and will change the level of combination between Ti and Ni-Cr alloy.

Biological safety of Ni-Cr alloy fabricated by laser solid forming technology / 第三军医大学学报

Objective To evaluate the biological safety of a Ni-62.9Cr-23 alloy fabricated by laser solid forming technology.Methods According to the requirements of national standards GB/T16886-2003,YY/T0279-1995 and YY/T0244-1996,general cytotoxicity,acute systemic toxicity,hemolysis testing,oral mucous membrane irritation testing were used to evaluate the alloy.Results The alloy was indicated having no cytotoxicity and with a hemolytic rate of 0.385%.The oral mucous membrane irritation testing showed that the alloy had no mucous membrane irritation.The acute systemic toxicity test indicated that the alloy had no acute systemic toxicity.Conclusion The Ni-62.9Cr-23 alloy has good biological safety in a certain extent.

A study of Ni-resistant bacteria isolated from gingival crevicular fluid on the patients wearing Ni-Cr alloy prosthesis (In terms of molecular biological aspects) / 대한치과보철학회지

As a material of metal-ceramic prosthesis, nickel as a form of Ni-Cr alloy has been used for many dental prostheses in many cases. However, several problems in use of the alloy have been revealed (ex ; tissue stimulation, skin allergy, hypersensitivity, cytotoxicity and carcinogenecity). Little is known about nickel with respect to the relationship between Ni-prosthesis and gaining of Niresistance in oral microorganisms. The present study was undertaken to check whether use of Ni-prosthesis leads to occurrence of Ni-resistant microorganisms. So this study may suggest the possible relationships between the oral microorganisms and nickel-resistance in oral environment. Bacteria were isolated from the gingival crevicular fluid on the patients wearing Ni-Cr prosthesis. The isolated bacteria were tested for their Ni-resistance in nickel containing media at different concentration from 3mM to 110mM. E. coli HB101 was used as control. The Ni-resistant bacteria were isolated and biochemically identified. The Ni-resistant bacteria were tested several biochemical, molecular-biological tests. Performed tests were; measuring the growth curve, antibiotic test, growth ability test in liquid media, isolation of the chromosome and plasmid, digestion of DNA by restriction enzyme, electrophoresis of chromosome and plasmid DNA, identification of Ni-resistant genes by the DNA hybridization. The results were as follows: 1) The bacteria isolated from gingival crevicular fluid on the patients wearing Ni-Cr alloy prosthesis showed nickel-resistance. 2) The isolated microorganisms grew at nickel containing media of high concentrations (60mM-110mM). 3) Based on the biochemical tests, the isolated microorganisms were identified as E nterococcus faecalis(13 cases), Klebsiella pneumoniae(1 case) and Enterobacter gergoviae(1 case). 4) Enterococcus faecalis expressed not only nickel resistance but also the multi-drug resistance to several antibiotics; chloramphenicol, kanamicin, streptomycin, lincomycin, clindamycin. However, all strain showed the sensitivity against the tetracycline. 5) DNA hybridization result suggests that there is no homology between the previously known gene of nickel resistance in Klebsiella pneumoniae and chromosomal DNA of Enterococcus faecalis.

The effect of veneer on the marginal fit of the copings using different materials / 实用口腔医学杂志

Objective:To compare the marginal fit changes between after-and before-veneering of the copings using three kinds of materials:gold alloy,cp titanium and Ni-Cr alloy,so as to determine whether the fit changes was influenced with the veneer and their clinical significance.Methods:24 maxillary incisor acrylic resin PFM abutments fabricated by machine with the consolidated standard were divided into three groups,each abutment was waxed-up,invested,and casted with three kinds of materials:gold alloy,cp titanium and Ni-Cr alloy.For all groups,the copings were repositioned on their respective abutments,the marginal fit values of four points of each coping were measured.Furthermore,after three groups of copings were veneered with recommended porcelain,marginal fit values of same point of each abutment were remeasured.SAS software was used to carry out statistical analysis.Results:One way analysis of variance of marginal fit values revealed significant differences between before and after veneering in three groups,and the marginal fit value enhanced after veneered.Among three groups,cp titanium group had a significant difference when compared with other two groups(P